The phosphate anion plays an important role in vivo. For example, in the signal transmission system, a variety of information transmissions can be controlled via the phosphate functional groups of phosphorylated proteins or phospholipids. It is therefore expected that an established sensing system for detecting phosphate anions in an aqueous solution corresponding to an in vivo environment will serve as a basic tool in cell biology and other fields for the analysis of a number of in vivo processes, the results thereof contributing to the development of new medicines and reagents. For example, the recognition of an intracellular phosphorylation signal, a key reaction for the malignant alteration caused by an abnormal information transmission, will be effective in designing inhibitors and the like against such reaction.
A potential useful means for detecting anions such as phosphate anion will be a fluorescent probe composed of a compound which exhibits fluorescence change upon being combined specifically with the anions. A number of probes have hitherto been developed for detecting cations typified by metal ions. However, with regard to fluorescent probes for detecting anions, only a small number of probes have been proposed which function in organic solvents, and there is found almost nothing for use in a neutral aqueous solution such as an in vivo media. This is because anions are generally larger in size than metal ions and are therefore more influenced by hydration, resulting in difficulty in chelation. In addition, while it is possible, with a probe for detecting metal ions, to develop fluorescence change via coordination of functional groups present in the structure of the fluorescent compound, such as aromatic amino groups, with metal ions, similar phenomena are unlikely to be utilizable in the detection of anions. For these reasons, very few examples are found of fluorescent probes for detecting anions such as phosphate anions.
One rare example of a fluorescent probe for recognizing phosphate anion in an aqueous solution is the ruthenium-bipyridylpolyaza compound reported by Beer et al. (P. D. Beer et al., Angew. Chem. Int. Ed., 40, 486 (2001); P. D. Beer et al., J. Am. Chem. Soc., 119, 11864 (1997)). However, this compound exhibits a very low fluorescence change. Another rare example is found in the utilization of a boronic acid-diester compound as a fluorescent probe for detecting anions such as phosphate ion (Japanese Patent Application Publication 2001-133407).
The object of the present invention is to provide a novel sensor composed of a fluorescent probe which is capable of detecting phosphate ion with a high sensitivity.